1. Field of the Invention
The present invention relates to a method for performing machining operations such as cutting and grinding operations on a workpiece, and to a mist supplying apparatus for use in the method.
2. Description of the Prior Art
In a machining operation such as a cutting or grinding operation, it is a conventional practice to supply a liquid to a machining part from a liquid supply nozzle extending thereto for dissipation of heat generated by contact between a workpiece and a machining tool. Where a large-scale stand-up machine tool such as a machining center is employed for the machining operation, however, the liquid and debris are liable to accumulate in a machined recess, thereby deteriorating the machining performance. When the workpiece is cut by intermittently bringing a carbide tool into contact with the workpiece, a machining point of a cutting edge of the tool is heated to a high temperature while the other portion thereof is cooled by the liquid supply. The repeated thermal shock may cause the cutting edge to chip (so-called chipping phenomenon) or crack.
For this reason, the cooling has recently been achieved by ejecting the liquid in a mist form, rather than as it is, toward the workpiece and the tool. Unlike the aforesaid direct liquid supply, this approach is free from the accumulation of the liquid in the machined recess and the chipping phenomenon due to the sudden cooling.
Another approach is to utilize a spindle of a machine tool for supplying a coolant to a machining part. In a tool mounting device as disclosed in Japanese Unexamined Patent Publication No. 10-29131 (1998), for example, a coolant supplied from a rotary joint 81 as a coolant supply source flows through a coolant channel (not shown) vertically extending through a drawbar 83 within a spindle 82, a coolant channel (not shown) vertically extending through a tool holder 84 and a coolant channel vertically extending through a tool (not shown), and then is ejected from a distal end of the tool as shown in FIG. 10.
Where the coolant to be employed in this device is in a liquid form, however, the accumulation of the liquid in the machined recess and the chipping phenomenon may occur as described above. Where the coolant is in a mist form, on the other hand, a liquid component of the coolant (which has a greater specific gravity than a gaseous component of the coolant) is liable to be forced toward the circumference of the drawbar 83 by a centrifugal force generated by high speed rotation of the drawbar when the coolant flows through the coolant channel within the drawbar 83. Therefore, the machining part cannot evenly be cooled or lubricated.
In view of the foregoing, it is an object of the present invention to provide a machining method and a mist supplying apparatus for use in the method, which can eliminate the problems associated with the direct liquid supply by ejection of a liquid in a mist form, and ensure homogeneous mixing of the liquid and air even with a construction utilizing a spindle of a machine tool.
In accordance with a first aspect of the present invention to achieve the aforesaid object, there is provided a method for machining a workpiece, which comprises the steps of: separately supplying compressed air and a liquid into a through-hole longitudinally extending through a drawbar within a spindle of a machine tool; allowing the compressed air and the liquid to separately flow through the through-hole; mixing the liquid with the compressed air in a distal end portion of the through-hole so as to make the liquid into a mist form; ejecting the resulting mist from a distal open end of the through-hole to deliver the mist to a distal end of a tool along an outer periphery of the tool or through the inside of the tool; and machining the workpiece while ejecting the mist from the distal end of the tool to supply the mist to a machining part.
In accordance with a second aspect of the present invention, there is provided a mist supplying apparatus, which comprises: a casing; a spindle rotatably supported within the casing and having a bore longitudinally extending therethrough; a drawbar disposed in the bore of the spindle for unitary rotation with the spindle and having a through-hole longitudinally extending therethrough; a tool holder detachably fixed to the drawbar; a tool detachably fixed to the tool holder; a compressed air channel and a liquid channel separately provided in the through-hole of the drawbar, the compressed air channel being supplied with compressed air from a compressed air supplier, the liquid channel being supplied with a liquid from a liquid supplier; and a channel provided in the tool holder; whereby the compressed air and the liquid are respectively ejected from the compressed air channel and the liquid channel so that the liquid is made into a mist form by the compressed air at an end of the drawbar adjacent to the tool holder, and the resulting mist is delivered to a distal end of the tool through the channel of the tool holder and along an outer periphery of the tool or through the inside of the tool so as to be ejected from the distal end of the tool.
In the machining method according to the present invention, the compressed air and the liquid are separately supplied into the through-hole longitudinally extending through the drawbar within the spindle of the machine tool, and allowed to separately flow through the through-hole when the workpiece is machined. When the compressed air and the liquid flow in an unmixed state through the through-hole of the drawbar rotating at a high speed, the centrifugal force generated by the high speed rotation may influence the compressed air and the liquid, but the mixing of the compressed air and the liquid thereafter carried out is not adversely affected. In addition, the liquid is mixed with the compressed air in the distal end portion of the through-hole so as to be made into a mist form. Then, the resulting mist is ejected from a distal open end of the through-hole, and supplied to the distal end of the tool along the outer periphery of the tool or through the inside of the tool. The machining operation is performed, while the mist is ejected from the distal end of the tool toward the machining part. Where the liquid is thus supplied in a mist form to the machining part, the accumulation of the liquid in a machined recess and the chipping phenomenon due to sudden cooling can be avoided which may otherwise occur in the case of the direct liquid supply. On the other hand, the mist supplying apparatus according to the present invention provides the same function and effect as the inventive machining method. The term xe2x80x9cmachining partxe2x80x9d herein means, for example, a surface of the tool involved in the machining operation and a surface of the workpiece being machined. In the present invention, the mist may be supplied to the distal end of the tool along the outer periphery of the tool as well as through the inside of the tool.
Where a mixture of a cooling liquid and a cutting liquid is supplied as the liquid into the through-hole in the inventive machining method, a cooling effect and a lubricating effect can simultaneously be provided to the machining part. Where the inventive mist supplying apparatus is adapted to supply a mixture of the cooling liquid and the cutting liquid into the liquid channel, the same function and effect can be ensured.
Where the cooling liquid and the cutting liquid are separately supplied as the liquid into the through-hole and allowed to separately flow through the through-hole in the inventive machining method, the cooling liquid and the cutting liquid are not mixed until these liquids reach the distal end portion of the through-hole, so that degradation in the quality of these liquids is suppressed. In addition, the cooling liquid and the cutting liquid are made into a mist form and then mixed with each other in the distal end portion of the through-hole. Thus, the mixing of the cooling liquid and the cutting liquid is sufficiently carried out, thereby providing an excellent cooling effect and lubricating effect. Where a cooling liquid channel and a cutting liquid channel are separately provided as the liquid channel and a cooling liquid supply channel for supplying the cooling liquid to the cooling liquid channel from a cooling liquid supplier and a cutting liquid supply channel for supplying the cutting liquid to the cutting liquid channel from a cutting liquid supplier are separately provided in the inventive mist supplying apparatus, the same function and effect can be ensured.